The present invention relates generally to data processing of images and particularly to computer controlled processing of color or grey scale images displayed in a computer controlled display system.
Present computer systems provide many useful tools for displaying and processing color images, including those color images of natural scenes which may be obtained, for example, by photographing a natural scene and then by scanning the image into a color computer system. Graphic artists and others are increasingly using computers to prepare color images for reproduction in publications. In these circumstances, it is often necessary to process the color image in a computer system in order to improve the appearance of the image so that the final pre-press appearance of the image will produce acceptable reproductions in a publication. The processing of these images includes such standard prior art techniques as cropping, modifying the overall exposure of the image, modifying the overall color cast of the image (e.g. compensating for use of daylight film under incandescent lighting), and selective "painting" and touch-up of the images.
The touch-up or painting of images in a computer system is often done with the aid of a specialized computer program which is designed for manipulating color graphics; such computer programs include Adobe Photoshop.TM. from Adobe Systems Corporation of Mountain View, Calif., MacDraw.TM. from Claris Corporation of Santa Clara, Calif.; and other well known painting, drawing and photographic processing computer programs. These programs typically have a special capability which is often referred to as a "fill." The fill operation typically involves selecting a region of an image and then filling in that region with a selected color. This operation will completely flood the selected image with the new color thereby completely overwriting any prior color and consequently removing any shading or textures which appeared in the selected region The shading or textures is usually a result of slight differences in color across a small region of the image (it will be appreciated that small differences in grey scale shading will also have the same affect). These textures or shadings are destroyed in fill operations and thus it is often difficult to use a fill operation on an image of a natural scene due to the irregular shapes of objects (e.g. a tree) in nature which often appear in such natural scenes. Some computer programs, such as PaintWorks Gold.TM. from Activision of Mountain View. Calif., include the ability to exchange one color with another color. While this is somewhat more precise than a fill operation, this "exchange" operation does not preserve the shading and textures in a natural scene because there is a one for one exchange in going from a single color to another single color.
Other attempts in the prior art (e.g. Adobe Photoshop) to improve the region selection process and selective color modification process have included edge detection algorithms which attempt to determine the edge of an object in a natural scene, such as the edge of the sky formed by the viewer's perception of the sky meeting the horizon. These edge detection algorithms attempt to segment the image into regions by determining the natural boundaries of an object in a natural scene. Any modifications to that object can then be constrained to the interior of the edge as determined by the algorithm. Once the boundaries are defined, in this particular prior art operation, the only automatic modifications possible are, for example, of the hue (that is, color), which does not fully preserve the texture and shadings. In this prior art, manual color corrections are needed to modify the colors in a way that does preserve the texture and shadings. Therefore, assuming that the edge detection algorithm properly works (and it often does not) the automatic modification of natural images is typically not satisfactory.
While the prior art provides some methods for selectively improving the color of natural scenes as displayed on a computer system, the prior art does not provide a satisfactory automatic method for selectively modifying a range of colors which results in preserving a texture or shading (or a range of grey scale) in an image. Therefore, it is an object of the present invention to provide a method and apparatus for selecting a region in an image marked for modification, and for automatically modifying a first plurality of colors in an image displayed by a computer controlled display system on a display device so that the first plurality of colors is selectively modified to a second plurality of colors in a pleasing manner while retaining in the modification the shading and texture of that part of the original image and smoothly blending this modified part into the overall image, and at the same time improving the overall appearance of the image.